1. Field of the Invention
The present invention relates to a package for an integrated circuit.
2. Description of Related Art
Integrated circuits are typically housed within a package that is mounted to a printed circuit board. The package has conductive leads or pins that are soldered to the printed circuit board and coupled to the integrated circuit by a lead frame. One type of conventional IC package is a quad flat pack (QFP), which has a plurality of gull wing shaped leads that extend from each side of the package housing. The outward extension of the gull wing leads, allows the leads to be readily soldered and inspected after assembly to the printed circuit board. The gull wing shape of the leads also compensates for any deviation in flatness between the printed circuit board and the package.
Another common type of package is a pin grid array (PGA) which has a matrix of output pins across the bottom surface of the package. The pin grid array increases the I/O of the package. PGA packages are difficult to inspect and may result in poor solder joints, if there is a discrepancy in the length of the pins and/or the flatness in the package or printed circuit board.
U.S. Pat. Nos. 5,045,921 and 5,216,278 issued to Lin et al., disclose an integrated circuit package which has a plurality of solder balls that interconnect the package to a printed circuit board. The Lin package is commonly referred to as a ball grid array (BGA). The solder balls are attached to a polyimide based flexible circuit board which has a number of conductive traces and accompanying solder pads. The IC die is connected to the solder pads of the flexible circuit by wire bonds, and electrically coupled to the solder balls through conductive traces routed across the flexible circuit. Vias are formed in the polyimide to interconnect each side of the flexible circuit.
The integrated circuit die of the Lin packages are mounted to a substrate and enclosed by a rigid housing or lid, typically constructed from a molded plastic material. The solder balls are relatively flexible and can thus compensate for any lack of flatness in the printed circuit board or package. Additionally, the solder balls are assembled in a an array on the bottom of the package, and thus provide a relatively high throughput.
Newly developed integrated circuits are continually designed with larger I/O and power requirements than existing ICs. These requirements necessitate packages that are more thermally efficient and have a larger number of output pins. It would be desirable to have BGA packages which are thermally efficient and provide more I/O, than packages in the prior art.